1. Field of the Invention
The technical scope of the present invention is that of heating system for fluid transport pipes. The invention relates in particular to the subsea or land transportation of hydrocarbons over great distances.
2. Description of the Related Art
To transport fluids in cold environments, for example for the subsea transport of hydrocarbons, one technical solution consists in heating the pipes to avoid the formation of obstructions resulting from the fluid cooling. A minimal temperature must therefore be maintained by heating the transport pipe. Electrical heating may be implemented to this end.
The robustness of the heating equipment must be suited to the environmental conditions in which the transport pipe is to be placed. Subsea hydrocarbon transport pipelines may be installed at depths of up to several kilometers making them all the more difficult to access for any maintenance or repair operations. These same difficulties may be encountered for land pipelines laid in a hostile environment.
Electrical heating wires for the transport pipe are generally positioned on the hydrocarbon flow pipe and are arranged under a protective casing. A layer of thermal insulation arranged under the protective casing is generally provided around the electrical heating wires and around the hydrocarbon flow pipe, so as to promote the heat exchange with the inner pipe and limit losses to the exterior. A double-walled pipe, also called a “pipe-in-pipe”, comprises a metallic external protective casing arranged around an internal metallic casing forming the inner hydrocarbon flow pipe.
Once in place, the hydrocarbon transport pipes can be several tens of kilometers in length. As a result the electrical heating cables are also several tens of kilometers in length. The electric wires arranged along the transport pipe can, in particular, be assembled in series, thereby forming a line running along the pipeline. Three lines powered by a three-phase electrical power supply are, for example, connected to one end of the pipe to the three phases of the supply and are connected together at the other end of the pipe to form an electrically-balanced star assembly. Each of the three lines is generally formed of a plurality of electric cables mounted in series and linked together using electrical connectors. Several sets of three lines are thus arranged along the transport pipe and around its periphery, each constituting a heating circuit. Here, the heating system works by Joule effect, but this is also applicable when the heating comprises a magnetic component (inductive heating).
One problem, however, arises in the case of a defective connection between two wires. A full line becomes inoperative and thus also the heating circuit of which it is a part. The heating of the transport pipe is thus deteriorated despite the fact that the electrical safety components allow the lines associated with the defective line to be deactivated.
This problem concerning the faults in the electrical connections can occur for any type of section assembled end to end to form a pipeline. For straight sections that are typically 12 meters, 24 meters or 72 meters long, and which are assembled at sea on a pipe laying ship to gradually form the pipeline, the problem is all the greater in that it is impossible to act on the pipe after it has been installed on the sea bed.
It is further known that failures in electrical systems are in the majority linked to failures in the connections. The multiplication of wires and sections to produce a long length pipe thus leads to systems containing several tens of thousands of connections, thereby elevating the overall risk to an unacceptably high level.
For example, for a 100 km pipe laid in sections of 20 m, each incorporating 60 wires, there are 3000 connections per kilometer, therefore 300000 connections in all.
There would thus appear to be a need, with reference to pipes heated by electric wires, for the robustness of the electrical system to be improved with regard to faults in the electrical connections.